linux-kernel - Re: [PATCH 01/25] ASoC: sun8i-codec: Set up clock tree at probe time

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Date:   Mon, 5 Oct 2020 11:53:36 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Samuel Holland <samuel@...lland.org>
Cc:     Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Chen-Yu Tsai <wens@...e.org>, Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Ondrej Jirman <megous@...ous.com>, alsa-devel@...a-project.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/25] ASoC: sun8i-codec: Set up clock tree at probe time

On Wed, Sep 30, 2020 at 09:11:24PM -0500, Samuel Holland wrote:
> The sun8i codec is effectively an on-die variant of the X-Powers AC100
> codec. The AC100 can derive its clocks from either of two I2S master
> clocks or an internal PLL. For the on-die variant, Allwinner replaced
> the codec's own PLL with a connection to SoC's existing PLL_AUDIO, and
> they connected both I2S MCLK inputs to the same source -- which happens
> to be an integer divider from the same PLL_AUDIO.
> 
> So there's actually no clocking flexibility. To run SYSCLK at the
> required rate, it must be run straight from the PLL. The only choice is
> whether it goes through AIF1CLK or AIF2CLK. Since both run at the same
> rate, the only effect of that choice is which field in SYS_SR_CTRL
> (AIF1_FS or AIF2_FS) controls the system sample rate.
> 
> Since AIFnCLK is required to bring up the corresponding DAI, and AIF1
> (connected to the CPU) is used most often, let's use AIF1CLK as the
> SYSCLK parent. That means we no longer need to set AIF2_FS.
> 
> Since this clock tree never changes, we can program it from the
> component probe function, instead of using DAPM widgets. The DAPM
> widgets unnecessarily change clock parents when the codec goes in/out
> of idle and the supply widgets are powered up/down.
> 
> Signed-off-by: Samuel Holland <samuel@...lland.org>

Acked-by: Maxime Ripard <mripard@...nel.org>

Maxime

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